News Release

CAMBRIDGE, Mass.--(BUSINESS WIRE)--Feb. 13, 2018--
Ra
Pharmaceuticals, Inc. (NASDAQ:RARX) (“Ra Pharma”) today announced
that it intends to offer and sell, subject to market and other
conditions, $50 million of its common stock in an underwritten public
offering. Ra Pharma expects to grant the underwriters a 30-day option to
purchase up to $7.5 million of additional shares of its common stock.

Credit Suisse, Jefferies, and BMO Capital Markets are acting as joint
book-running managers for the offering. SunTrust Robinson Humphrey is
acting as lead manager.

Ra Pharma intends to use the net proceeds from the offering, in addition
to our existing cash resources, to fund its Phase 2 trial for RA101495
for gMG, other pipeline programs, and for working capital and general
corporate purposes.

The securities described will be offered by Ra Pharma pursuant to a
shelf registration statement on Form S-3 (No. 333-221266), including a
base prospectus. The securities will be offered only by means of a
prospectus. A preliminary prospectus supplement related to the offering
and a final prospectus related to the offering will be filed with the
SEC and will be available on the SEC’s website located at www.sec.gov.
Copies of the preliminary prospectus supplements and the accompanying
prospectuses relating to the securities being offered may also be
obtained, when available, from: Credit Suisse Securities (USA) LLC,
Attn: Prospectus Dept., One Madison Avenue, New York, NY 10010, by
telephone at 800- 221-1037 or by email at newyork.prospectus@credit-suisse.com;
Jefferies LLC, Attn: Equity Syndicate Prospectus Department, 520 Madison
Avenue, 2nd Floor, New York, NY 10022, by telephone at 877-547-6340 or
by email at Prospectus_Department@Jefferies.com;
or BMO Capital Markets Corp., Attention: Equity Syndicate Department, 3
Times Square, New York, NY 10036, telephone: (800) 414-3627, email: bmoprospectus@bmo.com.

This press release shall not constitute an offer to sell or the
solicitation of an offer to buy these securities, nor shall there be any
sale of these securities in any state or jurisdiction in which such
offer, solicitation or sale would be unlawful prior to registration or
qualification under the securities laws of any such state or
jurisdiction.

About Ra Pharmaceuticals

Ra Pharmaceuticals is a clinical stage biopharmaceutical company
focusing on the development of next-generation therapeutics for
complement-mediated diseases. The Company discovers and develops
peptides and small molecules to target key components of the complement
cascade.

Forward-Looking Statement

This press release contains "forward-looking statements" within the
meaning of the Private Securities Litigation Reform Act of 1995,
including, but not limited to, statements regarding the completion and
anticipated proceeds of the proposed offering. All such forward-looking
statements are based on management's current expectations of future
events and are subject to a number of risks and uncertainties that could
cause actual results to differ materially and adversely from those set
forth in or implied by such forward-looking statements. These risks and
uncertainties related to fluctuations in our stock price, changes in
market conditions and satisfaction of customary closing conditions
related to the public offering, as well as the other factors discussed
in the “Risk Factors” section in Ra Pharma’s most recently filed Annual
Report on Form 10-K, as well as other risks detailed in Ra Pharma’s
subsequent filings with the Securities and Exchange Commission. There
can be no assurance that Ra Pharma will be able to complete the proposed
public offering on the anticipated terms. All information in this press
release is as of the date of the release, and Ra Pharma undertakes no
duty to update this information unless required by law.